Polymers are widely used for different water treatment applications such as flocculation, decantation, sludge thickening and conditioning and many others. Polymers, when properly activated (after the polymerisation phase) have the ability to develop ionic charges (positive or negative) and attract solids present in the different above-noted process. This reaction is commonly known as flocculation. Polymers are usually supplied as dry or liquid forms and are diluted to a certain concentration based upon available process equipment, to be used in the flocculation processes.
A problem with available systems used for diluting dry polymer, is that they do not actually offer a proven and cost effective method to validate polymer make-up concentration or polymer activation status. Therefore, during water treatment site visits and start-ups, many plant operators complain about their inability to obtain adequate information to validate quality and concentration or produced polymer solution.
A polymer is composed of many monomer units joined together via a chemical reaction called polymerization, or “activation of polymer”. The degree of polymerization is the number of monomer units in the chain. The chain can be very long—this tremendous length gives polymers some of their unique properties. The molecular weight of a polymer is the degree of polymerization multiplied by the molecular weight of the monomer unit. Acrylmide monomer has a molecular weight of 71. A polymer molecule with a degree of polymerization of 100,000 is made up of 100,000 acrylmide monomer units and will have a molecular weight of 7.1 million (100,000×71).
Organic or synthetic polymers (or polyelectrolytes) are essentially water soluble linear polymers with molecular weights as low as a few hundred thousand and as high as ten million or greater. These products are characterized by the existence of ionized (electrically charged) site groups on the polymer molecule. The electrical charge on the polymer molecule can be negative (anionic), positive (cationic) or no charge (non-ionic).
To optimize a dry polymer's performance, it is important to effectively wet each individual particle of polymer. To accomplish this task requires that the polymer be dispersed prior to being introduced into water. Systems which merely meter polymer into a bowl of stagnant water fail to meet this first criteria, and polymer gelling occurs and additional extended mixing and aging is generally required. Reaching optimum polymer performance is difficult, if not impossible, after polymer gelling occurs. In preparing the proper water treatment polymer solution concentration, industry standard is between a 0.25% to 0.6% solution concentration. Preparing a solution concentration in excess of this can result in increased viscosities and more difficult handling of polymer solution. As viscosity increases, so does the aging time required to reach optimum polymer performance. Note that initial make-down solution concentration often is different than final feed concentration. Final feed concentration can be as low as 0.1%. To achieve final solution concentration, a post dilution system is provided downstream of the solution metering pump.
Standard recommended minimum aging is 30 minutes for simple to hydrate polymers. As a general rule, though, and for design purposes, a minimum of 45 to 90 minutes is recommended when preparing solution concentration of up to 0.5%. Anionic polymers (negatively charged) can be more difficult to hydrate than cationic polymers (positively charged). The general “rule of thumb” (an approximate value based on guess work) of anionic polymers is to double the aging time. The amount of mixing time strongly depends on the polymer being used and the water temperature (temperature below 10 to −15 degrees Celsius will requires additional mixing time). Simple to hydrate polymers should be mixed only long enough to prevent the polymer particles from settling out. These particles will not settle out after they have hydrated to the point where they cannot be seen. For more difficult polymers, longer mixing may be required. Over mixing will damage the polymer and reduce the polymer's effectiveness.
Polymers (ionic type) will increase conductance of water and this effect can be measured with a conductivity meter. Conductance variation is affected by the concentration of the ions and by the nature of polymers used. Conductivity variation is different for strong and weak electrolytes.
Also, viscosity increase can be correlated to polymer chain formation and activation process.
In Japanese patent application No JP 59166216 published Sep. 19, 1984 to the Japanese company Kubota for a “method for controlling supply of flocculant in waste water treatment”, waste water is aerated, and the electric conductivity of the water is measured before supplying the flocculant. Accordingly with this conductivity, the supplying amount of flocculant can be controlled. Into a re-aerating tank to be re-aerated, a polymer is supplied as a flocculant through a control mechanism at solid-liquid separation precipitation tank. In order to configure the control mechanism, the electric conductivity of the threaded water from the re-aeration tank is measured by a measuring device before adding the flocculant, the signal from the measuring device is supplied to a control panel and its signal pressure on measured electric conductivity degree is used for input to a flow rate control valve and to be connected to a polymer tank, as well as to control valves. While controlling in proportion to the increase and decrease of the electric conductivity of the treated water, the amount of polymer is also controlled.
This Kubota patent therefore consists of a method to control the addition of flocculant in a waste water treatment chain. The current technologies do not readily allow the control of flocculant addition to assist in solid/liquid separation. A measure of conductivity is taken in the waste water in the presence of chlorine ions before addition of flocculants. The introduction of flocculants produce a variation in the electrical conductivity and this variation enables addition of required chemical products (polymer+aluminum sulphate).
However, the Kubota method is used for control of the quantity of chemical products supplied to a waste water treatment method, by measuring the variation of conductivity produced by addition of several reacting agents with one another. Such a method cannot be readily used in industry, since the polymers and the coagulants (such as aluminum sulphate) are not prepared or used together and are not necessarily controlled by the same parameters.
In U.S. Pat. No. 7,532,321 issued May 12, 2009 to Strategic Diagnostics Inc. for “compositions and methods for the detection of water treatment polymers” ('321 patent), there is disclosed that water soluble polymers play a role in coagulation and flocculation for waste water and drinking water clarification. In aqueous systems, the level of active polymer is not simply a function of how much polymer has been added. Because polymers generally add cost to processes employing them, it is desirable to be able to use them efficiently. There is further disclosed in the '321 patent that polyacrylic acid-based polymers are used as water treatment polymers, such as for the treatment of industrial cooling water to prevent corrosion and mineral deposits, or scale.
Generally, active water treatment polymers remove dissolved minerals from cooling water by complexing with the minerals. Over time, the complexation sites of the water treatment polymer molecules become saturated. The polymer molecules then become“bound” or inactive and are unable to remove any additional minerals from the cooling water. To prevent corrosion and scale damage to machinery, as the water treatment polymers are inactivated they must be removed and replaced by active polymers. Thus, active polymers must be continually fed into the cooling water to replace the inactive polymers. Maintaining the proper feed level for the active polymers is essential for optimum performance of the cooling water system. An improper feed rate can lead to serious problems. For example, an insufficient amount of active polymer can result in the water treatment being overwhelmed by dissolved minerals, thereby causing severe corrosion or scale deposit. On the other hand, maintaining too high a level of the active polymer is expensive and results in an inefficient method for treating industrial cooling water.
In the '321 patent, it is recognized that although several methods are available for determining the concentration of polymer in an industrial cooling water system, these techniques are unsatisfactory because they only determine the concentration of total polymer, i.e., active plus inactive polymer, and do not provide information regarding the concentration of active polymer alone. Moreover, available methods suffer from a lack of specificity and/or sensitivity.
Existing tests detect any polyanionic material and do not distinguish between active and inactive polymer concentrations. In addition, these methods have a detection threshold of only about 50 ppm polymer. Therefore, the total amount of active sulfonated polymer in an industrial cooling water system cannot currently be inexpensively, rapidly or reliably determined. Furthermore, currently available methods collect a sample at a given point in time, thereby providing the operator with only a snap shot rather than a moving picture in a highly dynamic system that is seeing a tremendous amount of change caused by chemical and physical stresses to the treatment polymer.
Still in the '321 patent, there is disclosed that cationic polymers are used in several areas of industrial water treatment such as paper manufacture, effluent stream clarification, sludge dewatering, mineral process and others. When discharged into the environment, excessive amounts of cationic polymers may be problematic. It is therefore desirable to know, with specificity and precision, the amount of residual cationic polymer in a sample prior to discharge. Many currently available methods of determining cationic polymer concentrations in waste water and other water treatment systems suffer from a lack of specificity or sensitivity as with the sulfonated copolymer detection methods described above.
However, the '321 patent utilizes Raman spectroscopy to detect the presence or amount of water treatment polymer either directly or indirectly. The water treatment polymer to be detected can be either an active water treatment polymer or an inactive water treatment polymer.
Although water treatment polymers themselves are generally not detectable by Raman spectroscopy, the polymers may be modified in such a way that they include a chemical moiety that is detectable or the polymers can be combined with a tracer molecule that is detectable.
The water treatment polymer can be modified or designed to contain one or more functional groups that are detectable by Raman spectroscopy at a different frequency when in a non-complexed (active) and/or complexed (inactive) state. This allows the absolute amounts of total polymer, or alternatively, the relative amounts of active and/or inactive water treatment polymer to be calculated. The total amount of polymer can be calculated by using different levels of the active and inactive states and making a calibration curve. The relative amounts of the active and inactive states can then be ascertained by comparing the measured value to the calibration curve. Alternatively, the tracer can be used to quantitate the relative amounts of active and/or inactive water treatment polymer. A tracer can be chosen that does not bind to the water treatment polymer if the water treatment polymer is inactive. The tracer resonates in a Raman spectra at one frequency when the tracer is bound to the water treatment polymer and at a different frequency when the tracer is not bound to the polymer. Similarly, a tracer is chosen that does not bind to active water treatment polymer. The relative amounts of tracer are then determined by monitoring the appropriate Raman resonant frequencies and the concentration of inactive water treatment polymer in a sample is calculated.
In a variation, one can employ a tracer that is indicative of the initial dosage. In this variation, the tracer does not bind to anything, but is blended into the product at a fixed ratio and thus is indicative of total product added. One can employ another tracer that binds an “active” chemical or is only available when the “active” chemical is available. By testing for the amount of this other tracer, one can deduce the rate and degree of degradation of polymer. Alternatively and/or additionally, it can be used to adjust the dosage of other additives.
In a further variation, relative concentrations of both active and inactive water treatment polymers in a sample are determined using one or more tracers. For example, one tracer is added that binds to both active and inactive water treatment polymer, but is detected by Raman spectroscopy at one wavelength when bound to active polymer and detected at a different wavelength when bound to inactive polymer.
In U.S. Pat. No. 6,750,328 issued Jun. 15, 2004 to Strategic Diagnostics Inc. for “antibodies for detection of water treatment polymers” ('328 patent), reference is made to antibody assays, and more particularly, to monoclonal antibodies and antibody assays for the detection of cationic, anionic and non-ionic water treatment polymers. In this '328 patent, it is recognized that although several methods are available for determining the total concentration of sulfonated copolymer in an industrial cooling water system, i.e., active plus inactive sulfonated copolymer, these techniques are unsatisfactory since they only determine the concentration of total sulfonated copolymer, and do not measure the concentration of the active sulfonated copolymer. Moreover, these methods suffer from lack of specificity or poor sensitivity.
In the '328 patent, it is recognized that cationic polymers are also useful in many areas of industrial water treatment. These areas include sludge dewatering, and many others. Excessive amounts of cationic polymers may cause problems in waters discharged to the environment. It is therefore recognized to be desirable to know with specificity and precision the amount of residual cationic polymer in a sample. Many prior art methods of determining cationic polymer concentrations in waste water and other water treatment systems suffer from lack of specificity or poor sensitivity as with the sulfonated copolymers described above. Monoclonal antibodies distinguish between an “active” and an “inactive” solution of sulfonated copolymer.